Abstract
Baker Engineering and Risk Consultants, Inc. (BakerRisk) has performed quantitative risk analyses (QRAs) for many facilities including companies handling anhydrous ammonia and other toxic materials. This paper compares several methods of estimating toxic risk exposure to personnel located within buildings.
Historically, toxic risk impacts have been assessed simplistically by developing geographic contours for threshold values and applying corresponding vulnerability values for personnel within those areas (e.g., a dose function is applied by assuming an exposure time). Building occupants were treated in a similar manner as outdoor personnel, although mitigation factors were often applied to credit toxic gas detection, ventilation isolation, and protective equipment such as escape packs.
Using a detailed method of evaluating toxic risks to personnel in buildings accounts for the calculated concentration at the building for each scenario, ventilation intake rate, ventilation isolation reliability, leak tightness of the building, lethality of the toxin, duration of the release, protective equipment, and clean purge air supplies, as applicable. In addition, rather than plotting the impact area and assessing it in a series of directions, the detailed method calculates the probability of directionalities of interest. This eliminates issues with long, narrow toxic plume “petals” that can result in toxic risks being underestimated.
This presentation provides an overview of simple vs. detailed toxic risk analysis methods. An example case will show how calculations are performed and how results are presented. A series of sensitivities will be discussed to explain how effective various potential mitigation strategies would be in improving safety.
